This application is based on Korea Patent Application No. 2001-86508 filed on Dec. 28, 2001 in the Korean Intellectual Property Office, the content of which is incorporated herein by reference.
(a) Field of the Invention
The present invention relates to an electronic active phase control array antenna for satellite communications. More specifically, the present invention relates to an electronic active phase control array antenna, a method for compensating for direction differences at the antenna, and a satellite tracking system and method using the antenna so as to resolve direction differences generated between two beams with different frequencies in the case of applying an electronic active phase control array antenna (referred to as an array antenna hereinafter) having two beams to broadband radio transmission and receiving methods.
(b) Description of the Related Art
FIG. 1 shows a conventional array antenna.
As shown, the array antenna comprises: an antenna 100; array antenna elements 102; phase shifters 103; and a signal combiner 104.
When incidence radio waves 101 that are incident to the antenna 100 reach the array antenna elements 102, the respective incidence radio waves 101 arrive at the array antenna elements 102 with different delay distances determined with respect to the directional angle xcex8.
For example, when each distance between the M array antenna elements 102 is set to be xe2x80x9cdxe2x80x9d, the propagation delay phase from a reference point is kMd sin xcex8. In this instance, since the propagation constant xe2x80x9ckxe2x80x9d is 2xcfx80f/c, a difference of the corresponding delay phase value is generated according to the frequency xe2x80x9cfxe2x80x9d, but since the conventional phase shifter 103 is used with a fixed predetermined frequency, a directional error caused by the frequency difference occurs in the external frequency of a predetermined frequency in the broadband case.
In another conventional technical configuration, a different phase shifter group may be installed below the phase shifters 103 so as to generate second beams, but in this case, since the second beams are generated using a calculated value fixed to a conventional predetermined frequency, the same directional errors occur.
In the identical manner, the same directional errors are generated in a structure for generating third or more than third beams because of the prior art configuration.
When the direction difference according to the prior art frequency difference is neglected as described above, since phase control codes that are calculated by fixing to a predetermined frequency are used for the respective frequencies without performing control through phase control codes independent of the respective component frequencies, the electronic beams of the antenna in broadband communications do not have a target directional angle xcex8 of the antenna""s actual target position 201 but rather they have a wrong target directional angle xcex8xe2x80x2 that directs a wrong target position 202, as shown in the example of the directional difference caused by the frequency difference shown in FIG. 2.
A single electronic beam phase is controlled with independent phase control codes with respect to the respective component frequencies by consideration of the above problem, and in this case, the frequency applied to the first beam cannot be used for a method for generating a plurality of beams with respective different frequencies, and the respective frequencies used to the second or greater beams cannot be applied to the propagation delay phase calculation equation kMd sin xcex8.
The directional difference according to the prior art frequency difference reduces the antenna""s satellite tracking gain and increases satellite tracking errors, and accordingly, the antenna gain cannot be effectively guaranteed and the satellite communication quality greatly worsens.
It is an object of the present invention to provide an electronic active phase control array antenna, a method for compensating for direction differences at the antenna, and a satellite tracking system and method using the antenna for considering directional differences according to frequency differences, and compensating for directional differences caused by the frequency differences and improving satellite communication quality when generating a plurality of beams with different frequencies.
In one aspect of the present invention, an electronic active phase control array antenna having two beams comprises: a first array unit for performing phase shifting on radio waves received via satellite communication, combining them, and generating first beams on the basis of a first phase delay control value according to a first beam frequency; and a second array unit for performing phase shifting on the output value phase-shifted by the first array unit on the basis of a second phase delay control value for compensating for the phase delay difference according to a second beam frequency shifted through the first array unit, and generating second beams.
The first array unit comprises: M array antenna elements for receiving radio waves via satellite communication, M representing a natural number; M first phase shifters for shifting phases of the radio waves respectively received through the M array antenna elements according to the first phase delay control value, and outputting results; M/2N first signal combiners for dividing the outputs of the M first phase shifters into N groups, combining outputs of the N divided groups, and outputting results, N representing a natural number of less than M; and a first beam signal combiner for combining the signals output from the M/2N first beam signal combiners to generate the first beams.
The second array unit comprises: M/2N second phase shifters for shifting the signals output from the M/2N first signal combiners according to the second phase delay control value, and outputting them respectively; and a second beam signal combiner for combining the signals output from the M/2N second phase shifters to generate the second beams.
In another aspect of the present invention, a method for compensating for directional differences using an electronic active phase control array antenna comprising a first array unit for performing phase shifting on radio waves received via satellite communication, combining them, and generating first beams on the basis of a first phase delay control value according to a first beam frequency; and a second array unit for performing phase shifting on the output value phase-shifted by the first array unit on the basis of a second phase delay control value for compensating for the phase delay difference according to a second beam frequency shifted through the first array unit, and generating second beams, comprises: assigning the first phase delay control code value of the first beam frequency so that the first beam may have a direction toward a first beam propagation incident direction; the second beam frequency passing through the first arraying unit to generate a phase delay according to a wrong second beam directional angle; and assigning the second phase delay control code value to generate a second phase delay corresponding to a second beam compensation moving angle generated by adding the second beam directional error angle to a second beam target moving angle of a second beam target directional angle.
The second phase delay control value is calculated from a value obtained by finding a second array phase control value with respect to a U coordinate axis and a second array phase control value with respect to a V coordinate axis, and linearly adding them when representing a directional two-dimensional plane as an antenna directional coordinate system that is the U and V coordinate.
The second beam positioned at a directional coordinate corresponding to the wrong second beam directional angle on the U and V coordinate system is moved to a second beam compensation moving directional coordinate and then it is compensated.
The movement of the second beam compensation moving direction is performed to a second beam compensation moving U vector component position and a second beam compensation moving V vector component position respectively vector-projected to the U and V coordinate axes with respect to the first beam directional coordinate.
In still another aspect of the present invention, a satellite tracking system cooperative with an electronic active phase control array antenna comprising a first array unit for performing phase shifting on radio waves received via satellite communication, combining them, and generating first beams on the basis of a first phase delay control value according to a first beam frequency; and a second array unit for performing phase shifting on the output value phase-shifted by the first array unit on the basis of a second phase delay control value for compensating for the phase delay difference according to a second beam frequency shifted through the first array unit, and generating second beams, comprises: a lookup table for representing a directional two-dimensional plane on an antenna directional coordinate system that is the U and V coordinates, and storing previously calculated U and V coordinate calculation values; a satellite tracking controller for receiving initial input data, performing desired first beam directional calculation on them, and outputting a first beam directional value and a corresponding frequency, and using the initial input data to perform a second beam directional calculation, and calculating a second calculation result parameter that is a second beam phase control value to output a second array phase control code value; a receiving beam controller for receiving the first beam directional value and corresponding frequency information output from the satellite tracking controller, calculating a first array phase delay control value for radio wave receiving, and outputting it to the first array unit; and a transmitting beam controller for receiving the first beam directional value and corresponding frequency information output from the satellite tracking controller, calculating a first array phase control value for radio wave transmission, and outputting it to the first array unit.